MUSEUM OF COMPARATIVE ZOOLOGY. 153 



examined. Hills formed of blown sand are prevailingly sharper, and 

 are more in alignment, than are these ridges of Central Florida. In no 

 case known to me do they enclose such large basins as those of the 

 Florida district. Indeed, it is rarely the case that the deposits are suf- 

 ficiently dense to retain water. Last of all, the fact that these undu- 

 lations generally disappear as we go to the north, gradually passing into 

 the uniform southern plain, is against the hypothesis of their formation 

 by wind action. There are no atmospheric circumstances which w'ould 

 make this central part of Florida the seat of extensive duning, while 

 such action was absent from the northern part of the peninsula. 



It appears to me that the most reasonable explanation of these tossed 

 sands is afforded by the supposition, which is apparently justified by 

 many facts, that the whole of Florida has recently been beneath the 

 level of the sea, and that during this period of submergence the Gulf 

 Stream swept across this portion of the peninsula, drifting the sands by 

 the action of its current into this complicated topography. The recent 

 submergence of the Floridian peninsula is indicated by the presence of 

 this large mass of detrital deposits of Pliocene or Post-Pliocene age. At 

 many points, as along the Indian River and elsewhere, these sands are 

 evidently overlying deposits containing altogether living species of ani- 

 mals. It is clear also that these sands have not been derived from the 

 erosion of sediments of an older date within the Florida district, but 

 have b'een imported from a distance. On this and other accounts we 

 may assume a recent submergence of the peninsula. Given this sub- 

 mergence without concomitant geographical changes which barred the 

 Gulf Stream from the Gulf of Mexico, we may suppose that the great 

 stream would have poured freely across the surface of the peninsula 

 within the region where we find this peculiar topography. Although 

 the Gulf Stream is confined at present within a narrow passage, where 

 it attains a speed of about four miles an hour, and possibly owes some- 

 thing of its rapidity of movement to the restriction of its exit, it would 

 doubtless, even with a larger opening, have a rate of movement suffi- 

 cient to exercise considerable energy on the bottom over which it flowed, 

 provided the floor was near the surface of the water. 



Nantucket Shoals, near Cape Cod, and other similar regions of 

 shallow sea underlaid by sand where the ocean has moderate tidal cur- 

 rents, show us that a topography in a general way like this of the lake 

 district may be formed under water. The researches of the Coast 

 Survey have shown that rapid movements of submarine sand in this 

 district are taking place. As the currents in this district rarely have a 



